Interpretive Summary: Previous studies have shown that Karnal bunt infected wheat plants are not randomly distributed throughout the field. In an effort to further understand the cause of this phenomenon, a study was conducted to determine the effects of field cultivation and tillage on the dispersal of soil borne spores originating from the first infected plant or first infected seed, to other parts of the field. A known number of Karnal bunt teliospores were sprayed onto a 1 X 3 m soil area in a naturally infested field in Arizona. A tractor drawn commercial disk was passed through the seeded area and soil samples were taken at measured intervals away from the initial area of infestation. This procedure was repeated 4 more times. Teliospores were recovered from each of the soil samples and counted. The experiment was repeated 3 times. Soil samples were collected prior to the start of the experiment in order to determine the background contamination level of the field. Teliospores were recovered to a maximum distance of 24 m; however, the numbers recovered from distances beyond 10 m were sporadic. Based on data from this research, we conclude that teliospores are not distributed in large quantities to great distances by tillage and therefore tillage cannot account for the spatial distribution of teliospores in many naturally infested Texas wheat fields.

Technical Abstract:
A study was conducted to determine the impact of tillage on dispersal of Tilletia indica teliospores from a concentrated point source in Arizona in November 2004. The infested source was created using a 300 ml teliospore suspension, containing approximately 90,000 teliospores per ml, sprayed onto a 1 × 3 m soil area. Approximately 400 g of soil were collected before tillage treatments, representing the teliospore baseline, and after each of 5 disk passes through the infestation source (n = 597). Soil sampling was conducted in each of three separate increments separated by 1, 3, or 10 m, to a total distance of 10, 30, and 50 m, respectively. Teliospores were recovered from soil samples by a combined size-selective sieving sucrose-centrifugation technique. Immediately following teliospore infestation, an average of 3.6 × 103 teliospores per 25 g soil sample were recovered from the three experimental infestation areas. Two different trends in recoverable teliospores occurred at 0 to 10 m sampling distances following 5 plow passes, either a decrease in the number of teliospores recovered, represented at points 0, 1, and 2 m, or an increase in recoverable teliospores found at points 3 to 10 m. The infested point source was repeated for a total of three experiments, and teliospores were recovered to a maximum distance of 24 m however, the numbers recovered from distances beyond 10 m were sporadic. Based on data from this research, we conclude that teliospores are not distributed in large quantities to great distances by tillage and therefore tillage cannot account for the spatial distribution of teliospores in many naturally infested Texas wheat fields.